1. Field of the Invention
The present invention relates to a slide bearing for a crankshaft of an internal combustion engine, which slide bearing is configured into a cylindrical shape by combining a pair of half bearings.
2. Description of Related Art
In general, a crankshaft of an internal combustion engine is supported, at each journal portion thereof, by a main bearing constituted of a pair of half bearings provided in a cylinder block lower portion of the internal combustion engine. In order to lubricate the main bearing, a lubricating oil is supplied by an oil pump into a lubricating oil groove formed in a circumferential direction in a inner peripheral surface of the main bearing, through an oil gallery formed in a cylinder block wall and a through-hole formed in a wall portion of the main bearing. The crankshaft also has a first lubricating oil passage which penetrates through the journal portion in a radial direction and of which both end openings communicate with the lubricating oil groove of the main bearing, a second lubricating oil passage which branches from the first lubricating oil passage to extend through a crank arm portion, and a third lubricating oil passage which connected with the second lubricating oil passage and penetrate through a crank pin in the radial direction so that both ends thereof open on an outer peripheral surface of the crank pin, whereby the lubricating oil supplied into the lubricating oil groove of the main bearing is further supplied into a lubricating oil groove formed in a circumferential direction on the inner peripheral surface of a connecting rod bearing for the crank pin portion of the crankshaft through the first lubricating oil passage, the second lubricating oil passage and the third lubricating oil passage (see JP-A-08-277831, for example).
At the time of initial operation of the internal combustion engine, foreign matters remaining in the lubricating oil passage, that is, swarf generated by metal processing at the time of cutting of the oil passage, molding sand at the time of molding and the like tend to mix into the lubricating oil which is supplied to the slide bearings for the crankshaft such as the aforementioned main bearing and connecting rod bearing. In the case of the conventional slide bearings for an internal combustion engine, these foreign matters accompany the flow of the lubricating oil on the bearings as the crankshaft rotates, but are discharged outside the bearings together with the lubricating oil through a gap formed between the bearings and a shaft portion by crush reliefs, chamfers and the like which are formed in end portions in a circumferential direction of the bearings.
As shown in FIG. 12, the aforementioned crush relief corresponds to a relief space 84 formed by reducing the thickness of the wall portion in the end portion region in the circumferential direction of a half bearing 80 by a relief depth RD in the radial direction from an original inner peripheral surface 82 (main circular arc) which is concentric with the center of rotation, and the relief space 84 is formed for absorbing positional displacement and deformation of butt end surfaces of the half bearings which may occur, for example, when the pair of half bearings are installed in the journal portion or the connecting rod of the crankshaft. Accordingly, the position of the center of curvature of the bearing inner peripheral surface in the end portion region in the circumferential direction of the half bearing in which the crush relief is formed differs from the position of the center of curvature of the bearing inner peripheral surface (main circular arc) in the remaining region (refer to SAE J506 (item 3.26 and item 6.4), DIN 1497, section 3.2, JIS D3102). The crush relief has a relief length RL, which is expressed as the height to an upper edge of the crush relief formation region from a horizontal surface, measured when the half bearing is placed so that both ends thereof in the circumferential direction are placed on the horizontal surface as lower end surfaces, and the relief depth RD is formed so as to be gradually smaller toward a central portion from the end portion in the circumferential direction of the bearing throughout the relief length RL.
In the conventional configuration, the relief length RL and the relief depth RD of the crush relief are constant along the entire half bearing in the axial direction (width direction) of the half bearing (see JP-A-2008-095858, paragraphs 0043, 0045, 0047 and the like, and JP-A-2005-069283).
JP-U-04-063810 shows another configuration of the crush relief where the relief length RL and the relief depth RD are not constant along the entire half bearing in the axial direction.